The present invention relates to a method for producing plants that are resistant to virus disease, to genetic material used in imparting such virus resistance, and to products of the method. Accordingly, the present invention involves applications from the fields of plant molecular biology, plant virology, and plant genetic engineering.
Virus infections in plants cause a variety of detrimental effects, including stunted growth, altered morphology, and reduced yields. In addition, virus infections often leave plants more susceptible to damage by other pests and pathogens. For general information on plant viruses, see, e.g., Matthews (1981), Lauffer (1981) and Kado and Agrawal (1972).
Plants do not have immune systems involving antibodies, like animals. However, plants have evolved several methods of resisting infection by pathogens. For example, some types of plants create lectins, which bind to saccharide moieties on the surfaces of invading fungi, and immobilize the fungi. In addition, some types of plants apparently create various molecules which circulate through the plant in response to attacks by bacteria, insects, and possibly viruses.
It is possible to induce some degree of virus resistance in some types of plants by infecting young plants with an xe2x80x9cattenuatedxe2x80x9d strain of a virus, i.e., a strain of the virus which does not cause severe symptoms; see, e.g., Rast (1972) and Costa (1980).
This approach has several limitations, including: (1) it can conveniently be used only in certain types of crops; (2) it can be used only with certain types of viruses; (3) it can be used only if a suitably attenuated strain of the infecting virus has been identified and isolated; (4) the protection provided by this method may be effective only against a limited number of different viruses; and (5) attenuated infection can severely aggravate an infection caused by a second, unrelated virus in a synergistic interaction.
There is, therefore, a need for a method of protecting plants from virus infection that overcomes the above-summarized problems and that does not require identification, isolation, or use of an attenuated virus. There is also a need for conferring virus resistance where natural genetic or cross-protection resistance is unavailable.
Accordingly, it is an object of the present invention to provide a method for producing virus resistant plants that does not depend on the use of an attenuated virus, the existence of a genetic determinant conferring resistance, or the availability of cross-protection.
It is also an object of the present invention to provide a method for genetically engineering plants by insertion into the plant genome of a DNA construct containing, inter alia, a small portion of a plant viral genome, such that the engineered plants display resistance to the plant virus.
It is another object of the present invention to provide a recombinant DNA molecule which can be used to produce genetically transformed, virus-resistant plants.
It is still another object of the present invention to provide genetically transformed cells and differentiated plants that are characterized, respectively, by the presence of a DNA sequence that causes the production of an RNA sequence of a plant virus.
In accomplishing the foregoing objects, there has been provided, in accordance with one aspect of the present invention, a method of producing genetically transformed plants which are resistant to infection by a plant virus, comprising the steps of
(a) inserting into the genome of a plant cell a recombinant, double-stranded DNA molecule comprising
(i) a promoter which functions in plant cells to cause the production of RNA sequences of the plant virus,
(ii) a DNA sequence derived from the plant virus that causes the production of an RNA sequence of the plant virus, and
(iii) a 3xe2x80x2 non-translated DNA sequence which functions in plant cells to cause the addition of polyadenylated nucleotides to the 3xe2x80x2 end the RNA sequence;
(b) obtaining transformed plant cells; and
(c) regenerating from the transformed plant cells genetically transformed plants which have increased resistance to infection by the plant virus.
In one preferred embodiment, the RNA sequence of the plant virus encodes a coat protein of that virus.
In accordance with another aspect of the present invention, there has been provided a recombinant, double-stranded DNA molecule comprising in sequence:
(a) a promoter which functions in plant cells to cause the production of RNA sequences of a plant virus;
(b) a DNA sequence derived from the plant virus that causes the production of an RNA sequence, the RNA sequence encoding the coat protein of the plant virus; and
(c) a 3xe2x80x2 non-translated region which functions in plant cells to cause the addition of polyadenylated nucleotides to the 3xe2x80x2 end of the RNA sequence.
There has also been provided, in accordance with another aspect of the present invention, bacterial and transformed plant cells that contain, respectively, DNA comprised of the above-mentioned elements (a), (b) and (c).
In accordance with yet another aspect of the present invention, a differentiated plant has been provided that comprises transformed plant cells, as described above, which exhibit resistance to the plant virus. According to still another aspect of the present invention, a process is provided that entails cultivating such a plant and, in addition, and propagating such plant using propagules such as explants, cuttins and seeds or crossing the plant with another to produce progeny that also display resistance to the plant virus.
Other objects, features and advantages of the present invention will become apparent from the following detailed description. It should be understood, however, that the detailed description and the specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.